Polyamide-imide resin insulating paint and insulation wire using the same

ABSTRACT

A polyamide-imide resin insulating paint according to the present invention includes polyamide-imide resin containing no halogen element in its molecular chain which is dissolved in a polar solvent, in which the polyamide-imide resin contains an aromatic diisocyanate component (A) having three or more benzene rings or an aromatic diamine component (E) having three or more benzene rings in a monomer, and a ratio M/N between a molecular weight (M) of the polyamide-imide resin per repeat unit and an average number (N) of amide groups and imide groups is equal to or more than 200.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/213,267, filed Jun. 17, 2008, the contents of which areincorporated herein by reference.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationserial no. 2008-002055 filed on Jan. 9, 2008, the content of which ishereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polyamide-imide resin insulatingpaint, and in particular, relates to a low-permittivity polyamide-imideresin insulating paint which can be obtained from a monomer having threeor more benzene rings, and an insulation wire using the paint.

2. Description of Related Art

These days, hybrid cars are becoming popular as the result of the energyconservation policies. To improve fuel economy in hybrid cars and motorperformance, drive motors are controlled by inverters and rapidlybecoming smaller, lighter, highly heat-resistant and are driven underhigher voltage. To meet a request for higher motor performance, such assmall size, light weight, and high heat resistance, windings currentlyused for the motor coil require polyamide-imide enameled wires whichhave excellent heat resistance, mechanical characteristics that canwithstand severe coil formation, and mission oil resistance. Themission-oil resistance greatly effects insulation-retaining capacitydepending on types and quantities of oil additives. However, ifinfluences of an oil additive are excluded, hydrolyzability due tomoisture absorption is directly related to mission-oil resistance.

On the other hand, a polyamide-imide resin insulating paint is aheat-resistant polymeric resin having heat resistance properties,excellent mechanical characteristics, and hydrolyzability resistanceproperties in which amide groups and imide groups are compounded at aratio of approximately fifty-fifty. Generally, the polyamide-imide resininsulating paint is created by a decarboxylation reaction of mainly twocomponents, 4,4′-diphenylmethane diisocyanate (MDI) and trimelliticanhydride (TMA), in a polar solvent, such as N-methyl-2-pyrolidone(NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), anddimethylimidazolidinone (DMI).

The isocyanate method and the acid chloride method are well-knownexamples of manufacturing methods for the polyamide-imide resininsulating paint. From the viewpoint of manufacturing productivity, theisocyanate method is usually utilized. An example of well-knownpolyamide-imide resin is one that is generated by a synthetic reactionof mainly two components which are 4,4′-diphenylmethane diisocyanate(MDI) and trimellitic anhydride (TMA) as an acid component. Furthermore,there is a method in which aromatic diamine and aromatic tricarboxylicanhydride react with each other under the acid excess condition at acompounding ratio from 50/100 to 80/100 in order to reformcharacteristics of polyamide-imide resin, and then polyamide-imide resinis synthesized by using a diisocyanate component (see JP-B-2897186).However, one of disadvantages of the film made of polyamide-imide resininsulating paint is its high permittivity. Due to the resin's structure,the existence of an amide group and an imide group significantly affectsthe increase in permittivity.

An insulation wire, specifically, an enameled wire used for a motor coiltends to be driven using an inverter to increase efficiency, andaccordingly, excessive voltage (inverter surge) is generated causingpartial discharge degradation to occur, resulting in insulationbreakdown in many cases. Furthermore, motor drive by high-voltagecoupled with the superposition of inverter surge increases the risk ofthe occurrence of partial discharge; therefore, it is becoming difficultto cope with insulation against inverter surge.

As a method of increasing voltage-applied service life by solving theproblem of partial discharge, technology of a partial-dischargeresistant enameled wire has been disclosed which is manufactured byapplying on a conductor a partial-discharge resistant resin paint whichis obtained by dispersing organo silica sol in a resin solution (e.g.,see JP-B-3496636 and JP-A-2004-204187). There is another method in whichan electric field between wires (electric field included in the layersof air present between wires) is eased to prevent partial discharge fromoccurring, thereby increasing a voltage-applied service life. The abovemethod is classified into two methods: one method in which an electricfield is eased by making wire surface conductive or semiconductive, andthe other method in which an electric field is eased by decreasingpermittivity of the insulation film.

However, the method in which the surface of an insulation wire is madeconductive or semiconductive has many problems and is not practicalbecause damage tends to occur during the coil winding process andinsulation characteristics are degraded, and an insulation proceduremust be conducted on the wire ends. On the other hand, with regard tothe method in which permittivity of the insulation film is decreased,since decrease in permittivity depends on the resin structure, it wasdifficult to acquire both heat resistance and excellent mechanicalcharacteristics simultaneously.

In a method described in JP-B-2897186, if2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and trimelliticanhydride (TMA) react with each other under the acid excess condition ata compounding ratio of 50/100 for the first stage synthetic reaction,due to the compounding ratio, acid anhydride preferentially reacts withan amino group than carboxylic acid; and furthermore, if a syntheticreaction proceeds, dehydration and imidization will occur, and bistrimellitic imide having carboxylic acid on both ends will be formed.

However, when a compounding ratio of BAPP is more than 50, a reactionbetween an amino group and TMA's carboxylic acid is hindered; therefore,even if a synthetic reaction is conducted at 200° C. which is theapproximate boiling point of NMP, the amino group remains, and resultsin forming a urea linkage of an amino group and an isocyanate groupduring the second stage synthetic reaction; consequently,characteristics are aggravated. Furthermore, when a compounding ratio ofBAPP is less than 50, acid anhydride remains during the first stagesynthetic reaction, water associated with an imidization reactionremains within the system, and acid anhydride turns into carboxylicacid; consequently, reactivity significantly decreases.

The characteristics aggravation problems are derived from impropercompounding balance of those functional groups. Accordingly,low-permittivity polyamide-imide which can cope with high-voltage driveis required to obtain excellent enameled wires.

SUMMARY OF THE INVENTION

Under these circumstances, it is an objective of the present inventionto provide a polyamide-imide resin insulating paint which has lowpermittivity and high partial discharge inception voltage whilemaintaining excellent heat resistance, mechanical characteristics, andoil resistance. Furthermore, it is another objective of the presentinvention to provide insulation wires using the same paint.

According to one aspect of the present invention, a polyamide-imideresin insulating paint includes polyamide-imide resin containing nohalogen element in its molecular chain which is dissolved in a polarsolvent, in which the polyamide-imide resin contains an aromaticdiisocyanate component (A) having three or more benzene rings or anaromatic diamine component (E) having three or more benzene rings in amonomer, and a ratio M/N between a molecular weight (M) of thepolyamide-imide resin per repeat unit and an average number (N) of amidegroups and imide groups is equal to or more than 200.

In the above aspect, the following modifications and changes can bemade.

(i) The polyamide-imide resin contains the aromatic diisocyanatecomponent (A), an aromatic diisocyanate component (B) having two or lessbenzene rings, and an acid component which comprises an aromatictricarboxylic anhydride (C) alone or comprises both the aromatictricarboxylic anhydride (C) and an aromatic tetracarboxylic dianhydride(D) simultaneously.

(ii) The polyamide-imide resin is made by mixing an aromatic imideprepolymer, which contains the aromatic diamine component (E) and anacid component comprising an aromatic tricarboxylic anhydride (C) and anaromatic tetracarboxylic dianhydride (D), with an aromatic diisocyanatecomponent (B) having two or less benzene rings.

(iii) A compounding ratio between the aromatic diisocyanate component(A) and an acid component comprising the aromatic tricarboxylicanhydride (C) alone or comprising both the aromatic tricarboxylicanhydride (C) and the aromatic tetracarboxylic dianhydride (D)simultaneously is A/(C+D)=50/100 to 70/100.

(iv) A compounding ratio between the aromatic diamine component (E) andan acid component comprising the aromatic tricarboxylic anhydride (C)and the aromatic tetracarboxylic dianhydride (D) is E/(C+D)=51/100 to70/100.

(v) A compounding ratio between the aromatic tricarboxylic anhydride (C)and the aromatic tetracarboxylic dianhydride (D) is C/D=100/0 to 60/40.

(vi) An insulation wire comprises a conductor and a film in which theabove-mentioned polyamide-imide resin insulating paint is applieddirectly on the conductor or on another insulation film and is baked toform the film.

Thus, a polyamide-imide resin insulating paint according to the presentinvention is created such that the polyamide-imide resin monomercontains an aromatic diisocyanate component (A) having three or morebenzene rings or an aromatic diamine component (E) having three or morebenzene rings, and a ratio M/N between the molecular weight (M) ofpolyamide-imide resin per repeat unit and the average number (N) ofamide groups and imide groups is equal to or more than 200; therefore,an abundance ratio between amide groups and imide groups contained inthe polymer, which greatly affects the increase in permittivity, isreduced; consequently, it is possible to reduce permittivity of thefilm.

Furthermore, when an aromatic diamine (E) is included in apolyamide-imide resin, by simultaneously using an aromatic tricarboxylicanhydride (C) and an aromatic tetracarboxylic dianhydride (D) as acidcomponents and synthesizing them, it is possible to suppress theformation of urea linkage caused by a reaction between residual aminogroups and isocyanate groups described in JP-B-2897186.

ADVANTAGES OF THE INVENTION

By using a polyamide-imide resin insulating paint according to thepresent invention for a film of an insulation wire, it is possible toachieve low-permittivity and increase partial discharge inceptionvoltage while maintaining general characteristics (heat resistance,mechanical characteristics, and oil resistance) equal to those ofversatile polyamide-imide enameled wires made by synthesizing MDI andTMA.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration showing a cross-sectional view of aninsulation wire having a film to which a polyamide-imide resininsulating paint according to the present invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, a preferred embodiment of polyamide-imide resin insulatingpaint according to the present invention will be described in detail.However, the present invention is not limited to the embodimentsdescribed herein.

The present invention is a polyamide-imide resin insulating paintincluding polyamide-imide resin containing no halogen element in itsmolecular chain which is dissolved in a polar solvent, wherein thepolyamide-imide resin monomer contains an aromatic diisocyanatecomponent (A) having three or more benzene rings or an aromatic diaminecomponent (E) having three or more benzene rings, and a ratio M/Nbetween a molecular weight (M) of the polyamide-imide resin per repeatunit and an average number (N) of amide groups and imide groups is equalto or more than 200. Furthermore, the polyamide-imide resin contains thearomatic diisocyanate component (A), an aromatic diisocyanate component(B) having two or less benzene rings, and an acid component whichcomprises an aromatic tricarboxylic anhydride (C) alone or comprisesboth the aromatic tricarboxylic anhydride (C) and an aromatictetracarboxylic dianhydride (D) simultaneously; or the polyamide-imideresin is made by mixing aromatic imide prepolymer, which contains thearomatic diamine component (E) and an acid component comprising thearomatic tricarboxylic anhydride (C) and the aromatic tetracarboxylicdianhydride (D), with the aromatic diisocyanate component (B) having twoor less benzene rings.

The polyamide-imide resin insulating paint according to the presentinvention is made by using a polar solvent, such asN-methyl-2-pyrolidone (NMP) or the like, as a main solvent and executingsolution polymerization. Other than NMP which is a main solvent,γ-butyrolactone, N,N-dimethylacetamide (DMAC), N,N-dimethylformamide(DMF), dimethylimidazolidinone (DMI), cyclohexanone, andmethylcyclohexanone, which do not inhibit synthetic reaction ofpolyamide-imide resin, can be used simultaneously as a solvent; and theNMP can be diluted using the solvent. Also, aromatic alkyl benzenes canbe simultaneously used for a dilution purpose. However, it is necessaryto carefully consider solvents which may decrease solubility ofpolyamide-imide.

From the viewpoints of characteristics and cost, polyamide-imide resin,which has been used most frequently for enameled wires, mainly includestwo components: 4,4′-diphenylmethane diisocyanate (MDI) as an isocyanatecomponent (B) and trimellitic anhydride (TMA) as an acid component (C).Generally, MDI and TMA are compounded at a fifty-fifty compounding ratioto synthesize a polyamide-imide resin, however, synthesis sometimesoccurs with a slightly excess isocyanate component within a rangebetween 1 and 1.05. This slightly excess isocyanate composition can alsobe applied to the reaction that uses isocyanate in the presentinvention.

As a diisocyanate component (B) having two or less benzene rings in themonomer, other than the above-exemplified 4,4′-diphenylmethanediisocyanate (MDI), for example, aromatic diisocyanate and its isomersand multimeric complexes, such as versatilely-used tolylene diisocyanate(TDI), naphthalene diisocyanate, xylylene diisocyanate, biphenyldiisocyanate, diphenyl sulfone diisocyanate, and diphenyl etherdiisocyanate can be applied. Also, according to necessity, aliphaticdiisocyanates, such as hexamethylene diisocyanate, isophoronediisocyanate, dicyclohexyl methane diisocyanate, and xylene diisocyanatecan be applied, or alicyclic diisocyanates hydrogenerated with thearomatic diisocyanate, exemplified above, and its isomers can also beused alone or simultaneously.

Aromatic diisocyanate components (A) having three or more benzene ringsin the monomer include 2,2-bis[4-(4-isocyanate phenoxy)phenyl]propane(BIPP), bis[4-(4-isocyanate phenoxy)phenyl]sulfone (BIPS),bis[4-(4-isocyanate phenoxy)phenyl]ether (BIPE), fluorene diisocyanate(FDI), 4,4′-bis(4-isocyanate phenoxy)biphenyl, and 1,4-bis(4-isocyanatephenoxy)benzene, and also include their isomers. By syntheticallyreacting those substances with aromatic diamine components having threeor more benzene rings in the monomer, exemplified below, aromaticdiisocyanate is manufactured. The manufacturing methods are notparticularly limited; however, methods that use phosgene are the mostdesirable from an industrial aspect.

Aromatic diamine components (E) having three or more benzene rings inthe monomer include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP),bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS),bis[4-(4-aminophenoxy)phenyl]ether (BAPE), fluorene diamine (FDA),4,4′-bis(4-aminophenoxy)biphenyl, and 1,4-bis(4-aminophenoxy)benzene,and also include their isomers.

Trimellitic anhydride (TMA) can be used as aromatic tricarboxylicanhydride (C) which is an acid component. Although other aromatictricarboxylic anhydrides, such as benzophenone tricarboxylic anhydride,can be used, TMA is most suitable. When synthesis is conducted by usingaromatic diamine (E) having three or more benzene rings in the monomer,it is desirable that aromatic tricarboxylic anhydride (C) andtetracarboxylic dianhydride (D) be simultaneously used.

As tetracarboxylic dianhydride (D), pyromellitic dianhydride (PMDA),3,3′4,4′-benzophenone tetracarboxylic dianhydride (BTDA),3,3′4,4′-diphenyl sulfone tetracarboxylic dianhydride (DSDA),4,4′-oxydiphthalic dianhydride (ODPA), and 3,3′4,4′-biphenyltetracarboxylic dianhydride can be exemplified. Also according tonecessity, butanetetracarboxylic dianhydride,5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, or alicyclic tetracarboxylic dianhydrides hydrogenerated witharomatic tetracarboxylic dianhydride, exemplified above, can be usedsimultaneously. Since reduction of permittivity and improvement oftransparency of resin composition can be expected by simultaneouslyusing an alicyclic structure substance, it may be used if necessary.However, the compounding quantity and chemical structure must becarefully considered to prevent a decrease in heat resistance.

It is desirable that a compounding ratio among an aromatic diisocyanatecomponent (A) having three or more benzene rings in the monomer,aromatic tricarboxylic anhydride (C), and aromatic tetracarboxylicdianhydride (D) be A/(C+D)=50/100 to 70/100 (molar ratio).

It is desirable that a compounding ratio among an aromatic diaminecomponent (E) having three or more benzene rings in the monomer,aromatic tricarboxylic anhydride (C), and aromatic tetracarboxylicdianhydride (D) be E/(C+D)=51/100 to 70/100 (molar ratio). When anaromatic diisocyanate component (A) is less than 50 and an aromaticdiamine component (E) is less than 51, during the first stage syntheticreaction, acid anhydride remains, water associated with an imidizationreaction remains within the system, and acid anhydride turns intocarboxylic acid, thereby significantly decreasing reactivity; therefore,that situation is undesirable. If an aromatic diamine component (E) ismore than 70, the compounding ratio of aromatic tetracarboxylicdianhydride (D) inevitably increases, accordingly imide groupssignificantly increase; consequently, mechanical and other excellentcharacteristics of polyamide-imide resin originated from amide groupsare adversely effected; therefore, that situation is undesirable. It isdesirable that a compounding ratio between the aromatic tricarboxylicanhydride (C) and aromatic tetracarboxylic dianhydride (D) be C/D=100/0to 60/40.

Furthermore, it is desirable that a ratio M/N between the molecularweight (M=weight-average molecular weight Mw) of synthesizedpolyamide-imide resin per repeat unit and the total number (N) of amidegroups and imide groups be equal to or more than 200. The lower thespecific permittivity becomes, the more desirable it is; and for theinverter surge insulation to become effective, it is desirable that thespecific permittivity be equal to or less than 3.5.

When synthesizing a polyamide-imide resin insulating paint, reactioncatalysts, such as amines, imidazoles, and imidazolines, can be used,and it is desirable that a reaction catalyst which does not disturb thestability of the paint be used. When a synthetic reaction is halted, asealant such as alcohol can be used.

EXAMPLES

The present invention will be described in more detail with referenceto, but is not limited to, the following examples and comparativeexamples.

Raw-material composition and features of the polyamide-imide resininsulating paint and characteristics of the obtained enameled wiredescribed in examples of the present invention and comparative exampleswill be shown in Tables 1 to 3 which will appear later in this document.

Examples 1 to 7 and Comparative examples 1 to 3 and 7 are examples ofthe synthesis of polyamide-imide resin insulating paint in which adiisocyanate component (A) is used for a polyamide-imide resin monomer,and the synthetic reaction was executed in the same manner as thesynthesis of ordinary polyamide-imide resin paint as shown below.

A flask equipped with a stirrer, reflux condenser tube, nitrogen inflowtube, and thermometer was prepared. Next, raw-materials and solvents,shown in Examples 1 to 7 and Comparative examples 1 to 3 and 7, werepoured into the flask at one time. Then, the mixture in the flask wasstirred in a nitrogen atmosphere, heated up to 140° C. for approximatelyone hour, and allowed to react at that temperature for two hours so thata polyamide-imide resin solution with a reduced viscosity ofapproximately 0.5 dl/g can be obtained (details will be described laterin this document).

Examples 8 to 14 and Comparative examples 4 to 6 are examples of thesynthesis of polyamide-imide resin insulating paint in which a diaminecomponent (E) is used for a polyamide-imide resin monomer, and syntheticreactions were executed in two stages as shown below.

A flask equipped with a stirrer, reflux condenser tube, nitrogen inflowtube, and thermometer was prepared. For the first stage syntheticreaction, a diamine component (E), shown in Examples 8 to 14 andComparative examples 4 to 6, acid components of aromatic tricarboxylicanhydride (C) and aromatic tetracarboxylic dianhydride (D), andapproximately 50 to 80% of solvent were poured into the flask; and themixture in the flask was heated up to 180° C. for approximately one hourwhile being stirred in a nitrogen atmosphere and was allowed to react atthat temperature for four hours while water generated by a dehydrationreaction was being discharged to the outside of the system. After theabove mixture was cooled to 60° C. in the same nitrogen atmosphere, adiisocyanate component (B) and remaining solvent were added to it. Forthe second stage synthetic reaction, the mixture was heated up to 140°C. for approximately one hour while being stirred in the nitrogenatmosphere, and was allowed to react at that temperature for two hoursso that a polyamide-imide resin solution with a reduced viscosity ofapproximately 0.5 dl/g can be obtained (details will be described laterin this document).

The polyamide-imide resin insulating paint was applied to a 0.8-mmcopper conductor and was baked. Then, an enameled wire with a 45-μmthick insulation film was obtained.

FIG. 1 is a schematic illustration showing a cross-sectional view of aninsulation wire having a film to which a polyamide-imide resininsulating paint according to the present invention is applied. As shownin FIG. 1, by applying a polyamide-imide resin insulating paint to aconductor 1 and baking it, an insulator film 2 can be obtained aroundthe surface of the conductor 1. Moreover, it is possible to form anotherinsulation film directly on a conductor 1, and then form a film 2 madeof polyamide-imide resin insulating paint according to the presentinvention. In this case, another insulation film is not particularlylimited as long as it does not disturb partial-discharge resistance orgeneral characteristics of the polyamide-imide resin insulating paint.

Characteristics (e.g., dimension, flexibility, abrasion resistance, heatresistance, and softening resistance) of the enameled wire were measuredby a method in accordance with JIS C 3003.

With regard to hydrolyzability resistance, 0.4-mL water and a twistedpair of enameled wires were put into a heat-resistant glass tube withinner volume of 400 mL, heated and melted by a burner and sealed; thenprocessed in a constant-temperature bath of 140° C. for 1,000 hours, andtaken out. Subsequently, insulation breakdown voltage was measured, anda remaining ratio was calculated for the insulation breakdown voltage ofanother twisted pair of enameled wires unprocessed the abovehydrolyzation treatment.

A metal electrode was deposited on the surface of an enameled wire, andcapacitance between the conductor and the metal electrode was measured;and then, based on the relation between the length of electrode and thethickness of film, specific permittivity was calculated. Capacitance wasmeasured at 1 kHz by using an impedance analyzer. With regard todry-time permittivity, the above-mentioned enameled wire was left in aconstant-temperature bath of 100° C. for 50 hours and capacitance wasmeasured while in the same bath. With regard to wet-time permittivity,the above-mentioned enameled wire was left in a thermo-hygrostat bath of25° C. and 50% RH (relative humidity) for 50 hours and capacitance wasmeasured while in the same bath.

With regard to partial discharge inception voltage, the above-mentionedenameled wire was left in a thermo-hygrostat bath of 25° C. and 50% RHfor 50 hours, and then discharge inception voltage was measured at 50 Hzwith a detection sensitivity of 10 pC.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Raw-material Diisocyanate BIPP 231.0 242.6 219.5 138.6composition component (A) (Mw = 462) (50.0) (52.5) (47.5) (30.0) ofhaving three or BIPS 338.8 polyamide- more benzene rings (Mw = 484)(70.0) imide resin BIPE 239.8 305.2 paint (Mw = 436) (55.0) (70.0) FDI40.0 (Mw = 400) (10.0) Diisocyanate 4,4′-MDI 125.0 118.8 62.5 112.5106.3 175.0 75.0 component (B) (Mw = 250) (50.0) (47.5) (25.0) (45.0)(42.5) (70.0) (30.0) having two or less 2,4′-MDI 12.5 benzene rings (Mw= 250) (5.0) 2,4′-TDI (Mw = 174) Tricarboxylic TMA 192.0 182.4 115.2172.8 163.2 192.0 192.0 anhydride (Mw = 192) (100.0) (95.0) (60.0)(90.0) (85.0) (100.0) (100.0) component (C) Tetracarboxylic PMDA 10.9dianhydride (Mw = 218) (5.0) component (D) BTDA 32.2 (Mw = 322) (10.0)ODPA 46.5 (Mw = 310) (15.0) DSDA 143.2 (Mw = 358) (40.0) Solvent NMP1600 1600 2000 1600 1700 1200 1350 γ-butyrolactone DMF 300 350 Featuresof Appearance Brown Brown Brown Brown Light Brown Brown polyamide- brownimide resin Reduced viscosity (dl/g) 0.51 0.49 0.52 0.50 0.51 0.50 0.52paint Nonvolatile content (wt %) 25.3 25.5 24.9 25.6 25.0 25.0 24.9Molecular weight per repeat unit (M) 920.0 982.8 1947.8 1042.7 1146.2835.2 968.4 Average number of amide groups and 4.0 4.2 6.7 4.4 4.7 4.04.0 imide groups per repeat unit (N) M/N 230.0 234.0 290.7 237.0 243.9208.8 242.1 A/(C + D) 50/100 52.5/100 70/100 55/100 57.5/100 30/10070/100 C/D 100 95/5  60/40  90/10   85/15 100 100 CharacteristicsDimension (mm) Diameter of 0.800 0.800 0.800 0.800 0.800 0.800 0.800 ofconductor polyamide- Thickness of film 0.045 0.046 0.046 0.045 0.0450.046 0.045 imide Overall diameter 0.890 0.892 0.891 0.890 0.890 0.8910.890 enameled Flexibility Winding of self Passed Passed Passed PassedPassed Passed Passed wire overall diameter of wire Abrasion Number of396 440 388 423 399 452 392 resistance reciprocating abrasion Heatresistance Insulation 73.0 78.0 68.3 79.0 77.8 74.2 77.6 (280° C. × 168h) breakdown remaining ratio (%) Hydrolyzability Insulation 88.9 90.052.3 89.7 87.4 90.0 90.2 resistance breakdown remaining (Water 0.1 vol%, ratio (%) 140° C. × 1000 h) Specific Dry-time 3.46 3.45 3.28 3.443.15 3.50 3.30 permittivity In constant- (1 kHz) temperature bath of100° C. Wet-time 3.85 3.80 3.48 3.67 3.35 3.99 3.56 (25° C. and 50% RH)Partial discharge (Vp) 920 942 993 950 1012 905 970 inception voltage(50 Hz, detection (25° C. and 50% RH) sensitivity: 10 pC)

Hereafter, specific descriptions will be provided.

Example 1

For Example 1, the following items were used: 231.0 g (0.5 mol) of BIPP(Mw=462) as an aromatic diisocyanate component (A) having three or morebenzene rings in the monomer, 125.0 g (0.5 mol) of 4,4′-MDI (Mw=250) asan aromatic diisocyanate component (B) having two or less benzene ringsin the monomer, 192.0 g (1.0 mol) of TMA (Mw=192) as an aromatictricarboxylic anhydride (C), and 1,600 g of NMP as a solvent. They weremixed and synthesized at 140° C., and a polyamide-imide resin insulatingpaint having reduced viscosity of approximately 0.5 dl/g and resinconcentration of approximately 25% by weight was obtained.

Example 2

For Example 2, the following items were used: 242.6 g (0.525 mol) ofBIPP as an aromatic diisocyanate component (A) having three or morebenzene rings in the monomer, 118.8 g (0.475 mol) of 4,4′-MDI as anaromatic diisocyanate component (B) having two or less benzene rings inthe monomer, 182.4 g (0.95 mol) of TMA as an aromatic tricarboxylicanhydride (C), 10.9 g (0.05 mol) of PMDA (Mw=218) as a tetracarboxylicdianhydride component (D), and 1,600 g of NMP as a solvent. They weremixed and synthesized at 140° C., and a polyamide-imide resin insulatingpaint having reduced viscosity of approximately 0.5 dl/g and resinconcentration of approximately 25% by weight was obtained.

Example 3

For Example 3, the following items were used: 338.8 g (0.7 mol) of BIPS(Mw=484) as an aromatic diisocyanate component (A) having three or morebenzene rings in the monomer, altogether 75.0 g (0.3 mol) of MDIcomprising 62.5 g of 4,4′-MDI (Mw=250) and 12.5 g of 2,4′-MDI (Mw=250)as an aromatic diisocyanate component (B) having two or less benzenerings in the monomer, 115.2 g (0.6 mol) of TMA as an aromatictricarboxylic anhydride (C), 143.2 g (0.4 mol) of DSDA (Mw=358) as atetracarboxylic dianhydride component (D), and 2,000 g of NMP as asolvent. They were mixed and synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Example 4

For Example 4, the following items were used: 239.8 g (0.55 mol) of BIPS(Mw=436) as an aromatic diisocyanate component (A) having three or morebenzene rings in the monomer, 112.5 g (0.45 mol) of 4,4′-MDI as anaromatic diisocyanate component (B) having two or less benzene rings inthe monomer, 172.8 g (0.9 mol) of TMA as an aromatic tricarboxylicanhydride component (C), 32.2 g (0.1 mol) of BTDA (Mw=322) as anaromatic tetracarboxylic dianhydride component (D), and 1,600 g of NMPas a solvent. They were mixed and synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Example 5

For Example 5, the following items were used: both 219.5 g (0.475 mol)of BIPP and 40.0 g (0.1 mol) of FDI (Mw=400) as aromatic diisocyanatecomponents (A) having three or more benzene rings in the monomer, 106.3g (0.425 mol) of 4,4′-MDI as an aromatic diisocyanate component (B)having two or less benzene rings in the monomer, 163.2 g (0.85 mol) ofTMA as an aromatic tricarboxylic anhydride component (C), 46.5 g (0.15mol) of ODPA (Mw=310) as an aromatic tetracarboxylic dianhydridecomponent (D), and 1,700 g of NMP as a solvent. They were mixed andsynthesized at 140° C., and a polyamide-imide resin insulating painthaving reduced viscosity of approximately 0.5 dl/g and resinconcentration of approximately 25% by weight was obtained.

Example 6

For Example 6, the following items were used: 138.6 g (0.3 mol) of BIPPas an aromatic diisocyanate component (A) having three or more benzenerings in the monomer, 175.0 g (0.7 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B) having two or less benzene rings in themonomer, 192.0 g (1.0 mol) of TMA as aromatic tricarboxylic anhydride(C), and 1,200 g of NMP as a solvent. They were mixed, synthesized at140° C., and diluted with 300 g of DMF, and then a polyamide-imide resininsulating paint having reduced viscosity of approximately 0.5 dl/g andresin concentration of approximately 25% by weight was obtained.

Example 7

For Example 7, the following items were used: 305.2 g (0.7 mol) of BIPEas an aromatic diisocyanate component (A) having three or more benzenerings in the monomer, 75.0 g (0.3 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B) having two or less benzene rings in themonomer, 192.0 g (1.0 mol) of TMA as an aromatic tricarboxylic anhydride(C), and 1,350 g of NMP as a solvent. They were mixed, synthesized at140° C., and diluted with 350 g of DMF, and then a polyamide-imide resininsulating paint having reduced viscosity of approximately 0.5 dl/g andresin concentration of approximately 25% by weight was obtained.

TABLE 2 Example Example Example Example Example Example 8 Example 9 1011 12 13 14 Raw-material Diamine component BAPP 215.3 194.8 225.5composition (E) having three (Mw = 410) (52.5) (47.5) (55.0) of or morebenzene BAPS 237.6 302.4 polyamide- rings (Mw = 432) (55.0) (70.0) imideresin BAPE 220.8 163.2 paint (Mw = 384) (57.5) (42.5) FDA 34.8 34.8 (Mw= 348) (10.0) (10.0) Diisocyanate 4,4′-MDI 118.8 75.0 106.3 106.3 112.5118.8 component (B) (Mw = 250) (47.5) (30.0) (42.5) (42.5) (45.0) (47.5)having two or less 2,4′-MDI benzene rings (Mw = 250) 2,4′-TDI 78.3 (Mw =174) (45.0) Tricarboxylic TMA 182.4 172.8 115.2 163.2 163.2 172.8 182.4anhydride (Mw = 192) (95.0) (90.0) (60.0) (85.0) (85.0) (90.0) (95.0)component (C) Tetracarboxylic PMDA 10.9 10.9 dianhydride (Mw = 218)(5.0) (5.0) component (D) BTDA 32.3 32.2 (Mw = 322) (10.0) (10.0) ODPA46.5 46.5 (Mw = 310) (15.0) (15.0) DSDA 143.2 (Mw = 358) (40.0) SolventNMP 1600 1500 1900 240 240 1200 1200 γ-butyrolactone 1360 1360 400 350DMF Features of Appearance Brown Brown Brown Brown Light Brown Brownpolyamide- brown imide resin Reduced viscosity (dl/g) 0.50 0.50 0.510.51 0.52 0.50 0.51 paint Nonvolatile content (w %) 24.7 25.6 24.9 25.025.3 25.2 24.6 Molecular weight per repeat unit (M) 982.8 998.5 1947.81125.6 1146.2 1003.4 950.5 Average number of amide groups and 4.2 4.46.7 4.7 4.7 4.4 4.2 imide groups per repeat unit (N) M/N 234.0 226.9290.7 239.5 243.9 228.0 226.3 A/(C + D) 52.5/100 55/100 70/100 57.5/10057.5/100 55/100 57.5/100 C/D 95/5  90/10  60/40   85/15  85/15 90/10 95/5  Characteristics Dimension (mm) Diameter of 0.800 0.800 0.800 0.8000.800 0.800 0.800 of conductor polyamide- Thickness of film 0.046 0.0460.045 0.045 0.046 0.045 0.046 imide Overall diameter 0.891 0.891 0.8900.890 0.891 0.890 0.891 enameled Flexibility Winding of self PassedPassed Passed Passed Passed Passed Passed wire overall diameter of wireAbrasion Number of 450 375 378 421 402 389 433 resistance reciprocatingabrasion Heat resistance Insulation 79.1 70.2 68.8 80.1 75.6 69.9 81.9(280° C. × 168 h) breakdown remaining ratio (%) HydrolyzabilityInsulation 89.0 60.3 51.3 88.5 87.7 86.3 90.5 resistance breakdownremaining (Water 0.1 vol %, ratio (%) 140° C. × 1000 h) SpecificDry-time 3.44 3.47 3.27 3.34 3.15 3.48 3.22 permittivity In constant- (1kHz) temperature bath of 100° C. Wet-time 3.83 3.81 3.48 3.51 3.34 3.953.44 (25° C. and 50% RH) Partial discharge (Vp) 930 933 986 980 1022 9041001 inception voltage (50 Hz, detection (25° C. and 50% RH)sensitivity: 10 pC)

Example 8

The following items were used for the first stage synthetic reaction ofExample 8: 215.3 g (0.525 mol) of BAPP (Mw=410) as an aromatic diaminecomponent (E) having three or more benzene rings in the monomer, 182.4 g(0.95 mol) of TMA as an aromatic tricarboxylic anhydride component (C),10.9 g (0.05 mol) of PMDA as an aromatic tetracarboxylic dianhydridecomponent (D), and 1,000 g of NMP as a solvent. They were mixed andsynthesized at 180° C. while water was discharged to the outside of thesystem, and then the mixture was cooled to 60° C. in the same nitrogenatmosphere. Then, for the second stage synthetic reaction, 118.8 g(0.475 mol) of 4,4′-MDI as an aromatic diisocyanate component (B) and600 g of NMP as a solvent were added to the above mixture, synthesizedat 140° C., and a polyamide-imide resin insulating paint having reducedviscosity of approximately 0.5 dl/g and resin concentration ofapproximately 25% by weight was obtained.

Example 9

The following items were used for the first stage synthetic reaction ofExample 9: 237.6 g (0.55 mol) of BAPS (Mw=432) as an aromatic diaminecomponent (E) having three or more benzene rings in the monomer, 172.8 g(0.9 mol) of TMA as an aromatic tricarboxylic anhydride component (C),32.2 g (0.1 mol) of BTDA as an aromatic tetracarboxylic dianhydridecomponent (D), and 1,000 g of NMP as a solvent. They were mixed andsynthesized at 180° C. while water was discharged to the outside of thesystem, then the mixture was cooled to 60° C. in the same nitrogenatmosphere. Then, for the second stage synthetic reaction, 78.3 g (0.45mol) of 2,4-TDI (Mw=174) as an aromatic diisocyanate component (B), and500 g of NMP as a solvent were added to the above mixture, synthesizedat 140° C., and a polyamide-imide resin insulating paint having reducedviscosity of approximately 0.5 dl/g and resin concentration ofapproximately 25% by weight was obtained.

Example 10

The following items were used for the first stage synthetic reaction ofExample 10: 302.4 g (0.7 mol) of BAPS as an aromatic diamine component(E) having three or more benzene rings in the monomer, 115.2 g (0.6 mol)of TMA as an aromatic tricarboxylic anhydride component (C), 143.2 g(0.4 mol) of DSDA as an aromatic tetracarboxylic dianhydride component(D), and 1,200 g of NMP as a solvent. They were mixed and synthesized at180° C. while water was discharged to the outside of the system, thenthe mixture was cooled to 60° C. in the same nitrogen atmosphere. Thenfor the second stage synthetic reaction, 75.0 g (0.3 mol) of 4,4′-MDI asan aromatic diisocyanate component (B), and 700 g of NMP as a solventwere added to the above mixture, synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Example 11

The following items were used for the first stage synthetic reaction ofExample 11: 220.8 g (0.575 mol) of BAPE (Mw=384) as an aromatic diaminecomponent (E) having three or more benzene rings in the monomer, 163.2 g(0.85 mol) of TMA as an aromatic tricarboxylic anhydride component (C),46.5 g (0.15 mol) of ODPA as an aromatic tetracarboxylic dianhydridecomponent (D), and both 240 g of NMP and 860 g of γ-butyrolactone assolvents. They were mixed and synthesized at 180° C. while water wasdischarged to the outside of the system, then the mixture was cooled to60° C. in the same nitrogen atmosphere. Then, for the second stagesynthetic reaction, 106.3 g (0.425 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B), and 500 g of γ-butyrolactone as a solventwere added to the above mixture, synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Example 12

The following items were used for the first stage synthetic reaction ofExample 12: both 194.8 g (0.475 mol) of BAPP and 34.8 g (0.1 mol) of FDA(Mw=348) as aromatic diamine components (E) having three or more benzenerings in the monomer, 163.2 g (0.85 mol) of TMA as an aromatictricarboxylic anhydride component (C), 46.5 g (0.15 mol) of ODPA as anaromatic tetracarboxylic dianhydride component (D), and both 240 g ofNMP and 860 g of γ-butyrolactone as solvents. They were mixed andsynthesized at 180° C. while water was discharged to the outside of thesystem, then the mixture was cooled to 60° C. in the same nitrogenatmosphere. Then, for the second stage synthetic reaction, 106.3 g(0.425 mol) of 4,4′-MD1 as an aromatic diisocyanate component (B), and500 g of γ-butyrolactoneas a solvent were added to the above mixture,synthesized at 140° C., and a polyamide-imide resin insulating painthaving reduced viscosity of approximately 0.5 dl/g and resinconcentration of approximately 25% by weight was obtained.

Example 13

The following items were used for the first stage synthetic reaction ofExample 13: 225.5 g (0.55 mol) of BAPP as an aromatic diamine component(E) having three or more benzene rings in the monomer, 172.8 g (0.9 mol)of TMA as an aromatic tricarboxylic anhydride component (C), 32.2 g (0.1mol) of BTDA as an aromatic tetracarboxylic dianhydride component (D),and 1,200 g of NMP as a solvent. They were mixed and synthesized at 180°C. while water was discharged to the outside of the system, then themixture was cooled to 60° C. in the same nitrogen atmosphere. Then, forthe second stage synthetic reaction, 112.5 g (0.45 mol) of 4,4′-MDI asan aromatic diisocyanate component (B), and 400 g of γ-butyrolactone asa solvent were added to the above mixture, synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Example 14

The following items were used for the first stage synthetic reaction ofExample 14: both 163.2 g (0.425 mol) of BAPE and 34.8 g (0.1 mol) of FDAas aromatic diamine components (E) having three or more benzene rings inthe monomer, 182.4 g (0.95 mol) of TMA as an aromatic tricarboxylicanhydride component (C), 10.9 g (0.05 mol) of PMDA as an aromatictetracarboxylic dianhydride component (D), and 1,200 g of NMP as asolvent. They were mixed and synthesized at 180° C. while water wasdischarged to the outside of the system, then the mixture was cooled to60° C. in the same nitrogen atmosphere. Then, for the second stagesynthetic reaction, 118.8 g (0.475 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B), and 350 g of γ-butyrolactone as a solventwere added to the above mixture, synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

TABLE 3 Compar- Compar- Compar- Compar- Compar- Compar- Compar- ativeative ative ative ative ative ative example 1 example 2 example 3example 4 example 5 example 6 example 7 Polyamide- Diamine componentBAPP 184.5 328.0 291.1 imide resin (E) having three (Mw = 410) (45.0)(80.0) (71.0) paint raw- or more benzene material rings compositionDiisocyanate BIPP 87.2 component (A) (Mw = 462) (20.0) having three ormore benzene rings Diisocyanate 4,4′-MDI 250.0 250.0 250.0 137.5 50.072.5 200.0 component (B) (Mw = 250) (100.0) (100.0) (100.0) (55.0)(20.0) (29.0) (80.0) having two or less 2,4′-MDI benzene rings (Mw =250) 2,4′-TDI (Mw = 174) Tricarboxylic TMA 192.0 144.0 115.2 192.0 192.0111.4 192.0 anhydride (Mw = 192) (100.0) (75.0) (60.0) (100.0) (100.0)(58.0) (100.0) component (C) Tetracarboxylic PMDA dianhydride (Mw = 218)component (D) BTDA 128.8 (Mw = 322) (40.0) ODPA (Mw = 310) DSDA 89.5150.4 (Mw = 358) (25.0) (42.0) Solvent NMP 1300 1450 1900 1500 1700 12001100 γ-butyrolactone 600 DMF 300 Features of Appearance Brown BrownPrecipitation Light Light Brown Brown polyamide- brown brown imide resinReduced viscosity (dl/g) 0.51 0.50 — 0.28 0.31 0.46 0.50 paintNonvolatile content (wt %) 25.2 24.9 — 25.4 25.0 25.7 25.2 Molecularweight per repeat unit (M) 354.0 791.0 812.0 — — 1083.8 792.8 Averagenumber of amide groups and 2.0 4.0 4.0 — — 6.8 4.0 imide groups perrepeat unit (N) M/N 177.0 197.8 203.0 — — 159.4 198.2 A/(C + D)  0/100 0/100  0/100 45/100 80/100  71/100  20/100 C/D 100 75/25 60/40 100 10058/42 100 Characteristics Dimension (mm) Diameter of 0.800 0.800 — 0.8000.800 0.800 0.800 of conductor polyamide- Thickness of film 0.045 0.046— 0.045 0.045 0.045 0.045 imide Overall diameter 0.890 0.891 — 0.8900.890 0.890 0.890 enameled Flexibility Winding of self Passed Passed —Failed Failed Failed Passed wire overall diameter of wire AbrasionNumber of 466 301 — 56 62 112 458 resistance reciprocating abrasion Heatresistance Insulation 78.2 72.2 — 65.1 21.2 63.3 75.0 (280° C. × 168 h)breakdown remaining ratio (%) Hydrolyzability Insulation 88.3 65.8 —14.1 13.8 55.2 89.2 resistance breakdown remaining (Water 0.1 vol %,ratio (%) 140° C. × 1000 h) Specific Dry-time 4.06 3.99 — 3.84 3.90 3.443.54 permittivity In constant- (1 kHz) temperature bath of 100° C.Wet-time 4.48 4.40 — 4.31 4.35 3.83 4.05 (25° C. and 50% RH) Partialdischarge (Vp) 833 848 — 854 849 923 889 inception voltage (50 Hz,detection (25° C. and 50% RH) sensitivity: 10 pC)

Comparative Example 1

For Comparative example 1, 250.0 g (1.0 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B), 192.0 g (1.0 mol) of TMA as an aromatictricarboxylic anhydride component (C), and 1,300 g of NMP as a solventwere used. They were mixed and synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Comparative Example 2

For Comparative example 2, 250.0 g (1.0 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B), 144.0 g (0.75 mol) of TMA as an aromatictricarboxylic anhydride (C), 89.5 g (0.25 mol) of DSDA as an aromatictetracarboxylic dianhydride component (D), and 1,450 g of NMP as asolvent were used. They were mixed and synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Comparative Example 3

For Comparative example 3, 250.0 g (1.0 mol) of 4,4′-MDI as an aromaticdiisocyanate component (B), 115.2 g (0.6 mol) of TMA as an aromatictricarboxylic anhydride (C), 128.8 g (0.4 mol) of BTDA as an aromatictetracarboxylic dianhydride component (D), and 1,900 g of NMP as asolvent were used. They were mixed and synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Comparative Example 4

The following items were used for the first stage synthetic reaction ofComparative example 4: 184.5 g (0.45 mol) of BAPP as an aromatic diaminecomponent (E) having three or more benzene rings in the monomer, 192.0 g(1.0 mol) of TMA as an aromatic tricarboxylic anhydride component (C),and 1,200 g of NMP as a solvent. They were mixed and synthesized at 180°C. while water was discharged to the outside of the system, then themixture was cooled to 60° C. in the same nitrogen atmosphere. Then, forthe second stage synthetic reaction, 137.5 g (0.55 mol) of 4,4′-MDI asan aromatic diisocyanate component (B), and 300 g of NMP as a solventwere added to the above mixture, synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Comparative Example 5

The following items were used for the first stage synthetic reaction ofComparative example 5: 328.0 g (0.8 mol) of BAPP as an aromatic diaminecomponent (E) having three or more benzene rings in the monomer, 192.0 g(1.0 mol) of TMA as an aromatic tricarboxylic anhydride component (C),and 1,200 g of NMP as a solvent. They were mixed and synthesized at 180°C. while water was discharged to the outside of the system, then themixture was cooled to 60° C. in the same nitrogen atmosphere. Then forthe second stage synthetic reaction, 50.0 g (0.2 mol) of 4,4′-MDI as anaromatic diisocyanate component (B) and 500 g of NMP as a solvent wereadded to the above mixture, synthesized at 140° C., and apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Comparative Example 6

The following items were used for the first stage synthetic reaction ofComparative example 6: 291.1 g (0.71 mol) of BAPP as an aromatic diaminecomponent (E) having three or more benzene rings in the monomer, 111.4 g(0.58 mol) of TMA as an aromatic tricarboxylic anhydride component (C),150.4 g (0.42 mol) of DSDA as an aromatic tetracarboxylic dianhydridecomponent (D), and 1,200 g of NMP as a solvent. They were mixed andsynthesized at 180° C. while water was discharged to the outside of thesystem, then the mixture was cooled to 60° C. in the same nitrogenatmosphere. Then, for the second stage synthetic reaction, 72.5 g (0.29mol) of 4,4′-MDI as an aromatic diisocyanate component (B), and 600 g ofγ-butyrolactone as a solvent were added to the above mixture,synthesized at 140° C., and a polyamide-imide resin insulating painthaving reduced viscosity of approximately 0.5 dl/g and resinconcentration of approximately 25% by weight was obtained.

Comparative Example 7

For Comparative example 7, the following items were used: 87.2 g (0.2mol) of BIPP as an aromatic diisocyanate component (A) having three ormore benzene rings in the monomer, 200.0 g (0.8 mol) of 4,4′-MDI as anaromatic diisocyanate component (B) having two or less benzene rings inthe monomer, 192.0 g (1.0 mol) of TMA as an aromatic tricarboxylicanhydride (C), and 1,100 g of NMP as a solvent. They were mixed andsynthesized at 140° C., diluted with 300 g of DMF, and then apolyamide-imide resin insulating paint having reduced viscosity ofapproximately 0.5 dl/g and resin concentration of approximately 25% byweight was obtained.

Comparative example 1 shows a versatilely used polyamide-imide enameledwire wherein flexibility, abrasion resistance, heat resistance, andhydrolyzability resistance are good; however, specific permittivity ishigh, and partial discharge inception voltage is low.

On the other hand, polyamide-imide enameled wires according to Examples1 to 14 have low dry-time permittivity which is equal to or less than3.5, and it was verified that partial discharge inception voltageincreased by 70 to 200 V. Other general characteristics were as good asthose of conventional enameled wires.

In Comparative examples 2 and 3, an aromatic tetracarboxylic dianhydridecomponent was simultaneously used along with a versatilely usedpolyamide-imide, and the number of imide groups was increased. However,in Comparative example 2, dry-time permittivity decreased only slightly,abrasion resistance decreased a little, and major effects could not beobtained. In Comparative example 3, because the number of imide groupsincreased, solubility became worse and precipitation occurred during theprocess of making paint.

In Comparative example 4, a compounding ratio of BIPP was set at 45, andreduced viscosity of paint, which is a molecular weight, did notincrease, and a high-molecular form was not created even in the enamelfilm. Consequently, flexibility and abrasion resistance significantlydecreased. It was considered that TMA's excess acid anhydride turnedinto carboxylic acid due to water present within the system, therebydecreasing reactivity.

In Comparative example 5, a compounding ratio of BIPP was set at 80, andthe general characteristics of the product also greatly deteriorated. Itwas considered that excess amino groups reacted with isocyanate groups,causing many urea linkages, and therefore, general characteristics ofamide-imide could not be maintained.

In Comparative example 6, an aromatic tetracarboxylic dianhydridecomponent was simultaneously used, and a compounding ratio wasdetermined without the existence of excess acid anhydride and aminogroups. However, because a compounding ratio of BIPP exceeded 70, theimide ratio increased, causing rigidity to increase and flexibility todecrease.

In Comparative example 7, a ratio M/N between the molecular weight (M)of polyamide-imide resin for one repeat unit and the total number (N) ofboth amide groups and imide groups was less than 200; and dry-timepermittivity exceeded 3.5.

Although the invention has been described with respect to the specificembodiments for complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A polyamide-imide resin insulating paint,including a low permittivity polyamide-imide resin containing no halogenelement in its molecular chain which is dissolved in a polar solvent,wherein: the low permittivity polyamide-imide resin is made by mixing anaromatic imide prepolymer, which contains an aromatic diamine component(E) consisting of an aromatic diamine having three or more benzene ringsin a monomer and an acid component consisting of an aromatictricarboxylic anhydride (C) and an aromatic tetracarboxylic dianhydride(D), with an aromatic diisocyanate component (B) consisting of anaromatic isocyanante having two or less benzene rings in a monomer,having a compounding ratio between C and D of C/D=95/5 to 60/40, acompounding ratio among E, C and D of E/(C+D)=51/100 to 70/100, and aratio M/N between a molecular weight (M) of the polyamide-imide resinper repeat unit and an average number (N) of amide groups and imidegroups is equal to or more than
 200. 2. The polyamide-imide resininsulating paint according to claim 1, wherein the low permittivitypolyamide-imide resin has a specific permittivity equal to or less than3.5.
 3. The polyamide-imide resin insulating paint according to claim 1,wherein: the aromatic diamine component (E) consisting of aromaticdiamine having three or more benzene rings in the monomer is at leastone selected from the group consisting of:2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP);bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS);bis[4-(4-aminophenoxy)phenyl]ether (BAPE); fluorene diamine (FDA),4,4′-bis(4-aminophenoxy)biphenyl; 1,4-bis(4-aminophenoxy)benzene andisomers thereof.
 4. The polyamide-imide resin insulating paint accordingto claim 1, wherein, the aromatic diamine component (E) consisting ofaromatic diamine having three or more benzene rings in the monomer is2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP).
 5. The polyamide-imideresin insulating paint according to claim 1, wherein the aromaticdiamine component (E) consisting of aromatic diamine having three ormore benzene rings in the monomer isbis[4-(4-aminophenoxy)phenyl]sulfone (BAPS).
 6. The polyamide-imideresin insulating paint according to claim 1, wherein the aromaticdiamine component (E) consisting of aromatic diamine having three ormore benzene rings in the monomer is bis[4-(4-aminophenoxy)phenyl]ether(BAPE).
 7. The polyamide-imide resin insulating paint according to claim1, wherein the aromatic diamine component (E) consisting of aromaticdiamine having three or more benzene rings in the monomer is a mixtureof 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and fluorene diamine(FDA).
 8. The polyamide-imide resin insulating paint according to claim1, wherein the aromatic diamine component (E) consisting of aromaticdiamine having three or more benzene rings in the monomer is a mixtureof bis[4-(4-aminophenoxy)phenyl]ether (BAPE) and fluorene diamine (FDA).9. An insulated wire, comprising a conductor and a film, wherein: thepolyamide-imide resin insulating paint according to claim 1 is applieddirectly on the conductor or on another insulation film and is baked toform the film.
 10. An insulated wire, comprising a conductor and a film,wherein: the polyamide-imide resin insulating paint according to claim 3is applied directly on the conductor or on another insulation film andis baked to form the film.
 11. An insulated wire, comprising a conductorand a film, wherein, the polyamide-imide resin insulating paintaccording to claim 4 is applied directly on the conductor or on anotherinsulation film and is baked to form the film.
 12. A polyamide-imideresin insulating paint, including a low permittivity polyamide-imideresin containing no halogen element in its molecular chain which isdissolved in a polar solvent, wherein: the low permittivitypolyamide-imide resin is made by mixing an aromatic imide prepolymer,which contains an aromatic diamine component (E) consisting of anaromatic diamine having three or more benzene rings in a monomer and anacid component consisting of an aromatic tricarboxylic anhydride (C) andan aromatic tetracarboxylic dianhydride (D), with an aromaticdiisocyanate component (B) consisting of an aromatic isocyanante havingtwo or less benzene rings in a monomer, having a compounding ratio amongE, C and D of E/(C+D)=51/100 to 70/100, and a ratio M/N between amolecular weight (M) of the polyamide-imide resin per repeat unit and anaverage number (N) of amide groups and imide groups is equal to or morethan 200.